The present invention relates to a semiconductor device and a manufacturing method thereof and specifically to a technique effectively applied to both of a Metal Insulator Semiconductor (MIS) type field effect transistor (MISFET) and a manufacturing technique of the same.
With the trend toward high speed and highly integrated semiconductor integrated circuits, it is required to make a gate insulating film of an MISFET thin. However, when an silicon oxide film with a low dielectric constant that is used a gate insulating film is made thin, there arises the problem that a gate leak current increases owing to direct tunneling.